Image intensifiers with inverter have fiber-optic plate (FOP), which turn the image over by 180
degrees. It also improves image quality. And it makes the device more compact and reduces the number
of optical parts in it. The output window of this image intensifier can be either flat or concave.
The devices made by «Novosibirsk Instrument-making plant» have image intensifier both with flat
output (binocular PN-11K) and with concave one (PN-15K, PN6K-4).